sleep fails for compiled program

[carl]

For the following program, runghc or ghci produces a list of numbers with a delay between printing each number. But when I run the compiled program, there is no delay.

import System.Posix
main = loop 10
loop 0 = print "done"
loop n = do
  print n
  sleep 3
  loop $ n - 1

[pcapriotti]

Thanks for the report.

[pcapriotti]

According to the man page of sleep:

sleep() makes the calling thread sleep until seconds
seconds have elapsed or a signal arrives which is not
ignored.

Since we use SIGVTALRM for the RTS clock, sleep is always going to be interrupted immediately. Normally, you should use threadDelay, which will also let other threads run (even without -threaded).

The attached patch explains this problem in the documentation for sleep, and adds a WARNING pragma.

[pcapriotti]

Pushed patch as ba7961f118f42ba9db7e5fba017270a257852ff3.